"I'm not 100 percent ready to get married," said Libertini, a 30-year-old cash officer. "I have asked my fiance every day for weeks if he wants to back out. I think the only thing keeping me in this is his mom and alcohol."

She said for the past two weeks the couple has been fighting and the pressure of planning their riverboat ceremony, which is only days away, is getting to her.

All couples have pre-wedding jitters, even the royals.

Watch a special "20/20" Thursday at 8 p.m. ET for a behind-the-scenes look at the life that awaits Kate Middleton, and join us again at 4 a.m. Friday for ABC News' live coverage of the Royal Wedding with Diane Sawyer and Barbara Walters.

When a British television show interviewed Lady Diana just days before her marriage to Prince Charles in 1981, the bride-to-be said she wasn't nervous about the walk down the aisle at St. Paul's Cathedral. "No," she said. "I get to go along with everybody else."

But by the end of the 15-minute interview going over the guest list and wedding details, Diana was "almost in fetal position, hunched in her chair, her arms wrapped around her middle, pulling distractedly at the fabric of her sleeves," according to the Telegraph newspaper.

Princess Diana and Prince Charles divorced in 1996, just a year before she was killed in a Paris car crash. Today half of all American marriages end in divorce.

Chances are Kate, who like Diana is marrying into the world of royalty and high expectation, is having pre-wedding nerves, say experts.

"In this situation with huge crowds and people all over the world watching her, I assume she has pretty severe jitters," said Jessica Barry, a wedding planner with Encore Creative in Tempe, Ariz.

"And there is the Princess Diana story, how she was so loved, and quiet and elegant and how she died tragically," she said. "Something in her mind must be feeling the pressure."

The jitters are common. "Sometimes the girls get extremely stressed out and go into Bride-zilla mode and the guys get all laid back and say they don't care, but they they want to know every detail about the wedding," said Barry. "They feel like they are in a completely foreign land."

Barry has shepherded more than 2,000 couples through the planning process and at least 60 have had feet cold enough to walk out -- some within 30 days of the wedding.

Since the economy turned sour, Barry said four to five couples a month change their mind. "I don't know if it's the finances or the pressure," she said.

Barry was working with one bride two weeks before the wedding when the groom-to-be bolted.

"I called the bride for final head count," she said. "She he was handling all the RSVPs. I called the groom to see how it was going. He said, 'I don't know how to tell you this, but I am no longer in Arizona. I just left. I walked out.' "

"We were all dying," said Barry, who had to break the news to the bride. "The poor girl. I told her I would take responsibility for calling the guests and venues and vendors, and I recommended she take the honeymoon. Better it was now than later."

Pre-Nuptual Jitters: Men Get Second Thoughts Too

"I think there is a common misconception that (particularly) men are likely to be commitment-phobic or to exercise cold feet because of fears of intimacy," said Jerrold Lee Shaprio, professor of counseling psychology at Santa Clara University in California.

"What is more likely is that the true underlying fear is not of committing, but of committing and being abandoned or rejected while emotionally vulnerable."

Anxiety does seem to be higher in males, he said.

Englishman Steven Wheatley found the love of his life -- American Shannon Woodward -- on the U.S.-U.K. dating website called I Love Your Accent.

They scheduled their wedding for April 29, the same day as the royal couple.

"It's put the extra pressure on," said Wheatley, 40, who works in banking. "I thought it would be our day... It didn't gel that we would be overshadowed by Prince William... Everyone else will be glued to the television set watching someone else's wedding."

The pair will marry in Naples, Fla., and and they still don't know on which side of the pond they will live as a married couple.

Woodward admits she has the jitters, "big time."

"This was supposed to be my day," she said. "Now there are two people who are more important than me and they don't even live here. The English pub in Naples is doing a whole production in aid of their wedding!"

"I do have a little feeling of dread, rather than nerves," said Wheatley, though he has no doubts about his fiancee. "Was this a wise move?"

"I am stunned to this day how many women knew they were marrying the wrong guy as they were walking down the aisle," she said. "It happens all the time...It's hard to find women who called off their wedding."

Milford, 47, says she is now happily married to the right man, but she left her fiance at the age of 28, just months before the wedding.

"The age of 30 looks like a deadline for women, and it's not necessarily to have babies," she said. "It's the end of a decade and there is family pressure -- who are you dating. Your friends are all dating."

"A lot of women say they have been in a relationship with a guy and have been dating for a couple of years and like him. Deep down, they know they have invested too much time on this relationship and they don't want to back out and they think no one better will come along."

Nerves about the wedding day -- party planning details, if your uncle will get drunk at the wedding or if a divorced parent will behave himself -- are in natural, she said.

"But when you are having doubts about the relationship -- he has a hard time keeping a job down or spends too much money or drinks too much or we fight too much, that's a problem," she said. "So many women get caught up in canceling the party. What they need to do is cancel the relationship."

Months before the wedding, Milford mustered the courage to tell her mother and she knew that had made her decision final. "All you need is someone to give you permission in that ah-ha moment," she said.

"I remember the hearing the story of Princess Diana wanting out of the wedding and her sisters talked her out of it," she said. "In London this week, Kate and William's faces are on all the plates and coins. When Princess Diana expressed her doubts, they said, 'It's too late -- your face is already on the towels."

But the chances of Kate leaving William at the altar are slim -- 1,000 to 1, according to Bodog.com, the world's largest Internet bookmaker.

Even Lisa Libertini, who said she is more stressed out than Kate, working 50-hour days, six days a week to pull off her April 29 wedding, said with a good man, it's survivable.

"I think this past month has put so much stress on me," she said. "He's the guy. He gets a suit and shows up, and I am the one who does all the details.

"But I think that if he can stand me through probably the most stressful times of our lives and he can constantly calm me down and say, 'I love you," this will work out."